David's listed what he'd play when he went to bat, so I'm following suit (links will take you to amazon.com's site for each album, where you can listen to a sample at the bottom of the page):

First, a few situation-specific selections:

Situation: First AB of the game
Song: Mothership Connection, Parliament

Alright, alright! Star Child here! Put a glide in your stride and a dip in your hip and come on to the mothership!

This next one is more for the irony than anything else.
Situation: AB in a road game
Song: All About U, 2Pac

Every other city we go
Every other video
No matter where I go
I see the same ho

Situation: Late in the game when they're obviously going to bring in a specialty reliever
Song: For Whom The Bell Tolls, Metallica
This one takes about a minute to develop, getting progressively harder and harder, so it would be perfect for those occaisional key AB's late in the game.

Now, a few tunes for any old time:
Them Bones, Alice In Chains
It hits hard right away, and it's got that awesome scream right at the beginning.

Rush, Talib Kweli
It opens with the hook, "Feel the rush, Feel the rush," and it's got this horn lick in the backgound that reminds me a little of "Gonna Fly Now" of Rocky Training Montage fame. Plus, I've never heard Kweli at the ballpark, and, frankly, I'd like to someday.

Immigrant Song, Led Zeppelin
This fills the exact niche that is alredy covered by Them Bones, but the song's just too good to leave out.

Spottieottiedopaliscious, Outkast
What can I say? This is probably the smoothest hip-hop song I've ever heard. Another brilliant usage of horns with hip-hop. From the Aquemini album.

Hunting Bears, Radiohead
The beginning of this one is pretty much just an electric guitar playing a riff that sounds like something from the great Johnny Depp western, Dead Man. It's from the Amnesiac album, if anyone cares to give it a listen.

Finally,
Renegade, Styx
Oh, don't give me that. Everyone is a closeted Styx fan.

Hmmm, that makes nine. One more to give me a nice, round number:
Ring Of Fire, Johhny Cash
Pay your respects to the Man In Black!